Process and apparatus for the treatment of fibrous materials in the production of cellulose or semi-cellulose



H- HULLMANN CELLULOSE OR SEMI-CELLULOSE Filed July 7, 1958 MATERIALS INTHE PRODUCTION OF PROCESS AND APPARATUS FOR THE TREATMENT OF FIBROUSSept. 12, 1961 INVENTOR. 44m 4444......-

The process for the treatment of fibrous materials in the production ofcelluloseor semi-cellulose is known, in which the fibrous materials areimpregnated with d1- gesting liquid and digested under superatmosphericpressure in a digesting chamber with an addition of heat ng steam afterseparation from the surrounding digesting liquid. In this known process,the fibrous materials to be treated, for example wood chips, areintroduced in a continuous process into an impregnating chamber undersuperatmospheric pressure, in which they are impregnated with a hotsulphite liquor not exceeding a temperature of 120 C., which serves asdigesting liquid. The substances thus impregnated are thereafterseparated from the surrounding digesting liquid in this chamber andintroduced into a digesting chamber which is under a highersuperatmospheric pressure, and in which they are digested at atemperature of 160 to 205 C. with a supply of heat steam.

In addition, a known discontinuous process comprises the step ofexposing the fibrous materials to a vacuum for the purpose of drivingoff the air contained therein before the addition of the digestingliquid. The fibrous materials are thereafter digested in the liquidunder superatmospheric pressure.

The invention relates to a process for the treatment of fibrousmaterials in the production of cellulose or semicellulose in which thefibrous materials are impregnated with digesting liquid and, afterseparation from the surrounding digesting liquid, are digested undersuperatmospheric pressure in a digesting chamber with a supply ofheating steam, and has for its object to provide an improvement in theimpregnating operation with a simultaneous simplification of theientireprocess. In accordance with the invention, an" excess of digestingliquid is constantly circula ed in a circuit extending through a vacuumchamber and a pressure chamber under the digesting pressure, the fibrousmaterials to be treated being continuously fed to the said circuit,carried along with the digesting liquid and impregnated therewith in itstravel from the vacuum chamber to the pressure chamber, and finallyseparated from the surrounding digesting liquid before the digestingoperation in the pressure chamber.

As a result of the vacuum treatment, a good expulsion of the air fromthe fibrous materials is efiected. The

impregnating operation commences directly in the vacuum and is continueduntil the materials are brought to the disintegrating pressure of thedigesting chamber. The materials thus do not come into contact with airbetween the vacuum treatment and the digesting process. The

pressure increase during the impregnating operation furthermore gives agood penetration of the liquid into the fibrous materials. Owing to thegood preceding air extraction in the vacuum, however, an increasedtemperature of the impregnating liquid is not necessary.

The invention further relates to an apparatus for'carrying out theprocess according to the invention. In the. drawing a constructionalexample of such an arrangement is illustrated in simplified form, withreference to which the process will also be described by way of example.

Essential component parts of the apparatus are: a vacu- Sttes Patent umchamber 1, an impregnating vessel 2 having two up wardly extending limbs2 2 connected together at the bottom by a duct 2 a digesting vessel 3and a pump 4 disposed in the connecting duct 2 The limb 2 of theimpregnating vessel is connected at its upper end through afunnel-shaped pipe section 5 to the vacuum chamber 1, and the limb 2 isconnected through an inclined descending pipe 6 to the upper end of thedigesting vessel 3.

A vacuum pump 7 connected to the upper part of the vacuum chamber 1serves to extract the air and to maintain a pressure below atmosphericin this container.

The impregnating vessel 2 contains digesting liquid. The level of theliquid on the side of the limb 2 is situated at a point 8 in the vacuumchamber 1 and at a point 9 in the limb 2 The liquid level 8 is exposedto the vacuum of the chamber 1 and the liquid level 9 is exposed to thedigesting pressure prevailing in the digester 3. The pump 4 provided inthe duct 2 which is pref erably a centrifugal pump, continuously conveysdigesting liquid from the limb'Z into the limb 2 of the impregnatingvessel against the action of the pressure difference existing betweenthe digester 3 and the vacuum chamber 1.

An introduction container 10 is disposed at a lower level than thevacuum chamber and communicates through a duct 12 and valve 11 with astorage container 13 containing digesting liquid. The valve 11 is soregulated that the introduction container is always filled withdigesting liquid to a certain level. The liquid level in theintroduction container is then situated at a point 14 at which it isexposed to atmospheric pressure.

A substantially vertically arranged duct 15 extends at its lower end 16into the liquid contained in the introduction container 10 and opens atits upper end 17 into the vacuum chamber 1 above the liquid level 8. Theliquid is sucked up from the introduction container 19 into the vacuumchamber 1 by the vacuum effect. The upper end 17 of the duct 15 may lie,for example, about 8 m. above the liquid level 14. The vacuum in thechamher 1 then corresponds to this liquid column plus the pressure lossof the flow in the duct 15. The vacuum is so regulated by means of thepump 7 that a quantity corresponding to the liquid conveyed by the pump4 from the vacuum chamber into the limb 2 of the impregnation vessel isconstantly supplied through the duct 15, whereby the liquid level 8 isconstantly maintained at the same level.

A further duct 18 serves to return digesting liquid from the limb 2 ofthe impregnation vessel in order here also to maintain the liquid level9 at a constant height. The duct 18 is connected at one end to the limb2 at a point 19 and opens at its other end into the introductioncontainer 10 at a point 20. A valve 21 serves to regulate the refluxquantity. In order to utilise with advantage the pressure difierenceunder which the liquid flows back into the introduction container 10,there is provided in the reflux duct 18 a turbine 22 which thus suppliesa part of the driving energy for the pump 4. The remainder is suppliedby an electric motor 23 coupled to the pump 4.

The pump 4 thus continuously circulates an excess of 18 and having avalve 26 disposed therein and which,

when open, permits digesting liquid to flow from the limb 2 of theimpregnating vessel into the storage container 13 instead of into theintroduction container 19. The last-mentioned container is then alsoincluded in the circuit. The admission to the turbine 22 can be cut edby a further valve 27 arranged in the duct 18. A further duct 30 whichconnects a point 28 situated in the lower part of the limb 2 of theimpregnating vessel with the duct 18 and which is adapted to be closedoff by a valve 29 furthermore permits of extracting the returning liquidfrom this lower point 28 instead of from the point 19.

The fibrous materials to be treated, for example wood chips, areintroduced into a charging hopper 31 which extends at its lower end intothe digesting liquid contained in the introduction container 10. Thelower part of the duct 15, also dipping into the said liquid, is bentupward at about 180. The lower end 16 of the duct widens in the form ofa funnel and lies directly below the charging hopper 31, the clearancebetween the two being such, however, that digesting liquid can enter theduct 15. The fibrous materials then pass continuously from the charginghopper 31 into the duct 15 forming a component part,

of the liquid circuit and are carried along therein by the liquid streamand conveyed into the vacuum chamber 1.

The liquid delivery of the pump 4 and thus also the further quantity fedthrough the duct 15, is so great in relation to the entering quantity offibrous materials that the concentration of the latter in the liquidrising through the duct 15 is relatively low. However, it is desirablefor the fibrous materials to remain for a relatively long period in thevacuum chamber 1. The vacuum chamber 1 therefore comprises an innercontainer 32 below the point at which the duct 15 enters it. The bottomof the said container is provided with a central delivery branch 33which opens into the funnel-shaped pipe section connecting the limb 2 ofthe impregnation vessel with the vacuum chamber 1. A clearance 34 isleft between the inner container 32 and the delivery branch 33 on theone hand, and the jacket of the vacuum chamber 1 and the pipe section 5on the other hand.

The fibrous materials entering the vacuum chamber 1 are trapped in theinner container 32 up to a point 35 situated slightly below the mouth 17of the duct 15. The upper part of the inner container 32 is formed withapertures, so that the surplus liquid can escape into the clearance 34and can pass through the latter directly into the pipe section 5 andinto the limb 2 of the impregnation vessel. A delivery stirrer 36provided at the bottom of the inner container 32 and driven by means notshown, and a conveyor worm 37 disposed in the delivery branch 33 ensurea uniform ejection of the momentarily lowermost fibrous materials intothe pipe section 5, so that the materials contained in the innercontainer 32 always remain heaped up to the same level.

The fibrous materials delivered into the pipe section 5 pass into thelimb 2 of the impregnation vessel 2, and are carried along by the liquidsucked in by the pump 4, and entrained and impregnated thereby along thepath leading through the connecting duct 2 from the vacuum chamber ofthe chamber 1 into the space exposed to the digesting pressure in thelimb 2 of the impregnation vessel.

The impregnation chamber extends from the liquid level 8 in the vacuumchamber 1 tothe liquid level 9 in the limb 2 of the impregnation vessel.Thus, in the described apparatus, the fibrous materials are continuouslybrought, afiter the vacuum treatment, from a vacuum to the digestingpressure during the process of impregnation with the surroundingdigesting liquid.

The fibrous materials rising in the limb 2 of the impregnation vesselare taken up in the upper part of the latter by a conveyor worm 38driven by means not shown and conveyed to the point to which theobliquely descending pipe 6 is connected. They are thereby lifted abovethe liquid level 9 and'thus separated from the surrounding digestingliquid before falling through the pipe 6 into the digesting chamber ofthe digesting vessel. 3.

In the region of the point 19 of the limb 2 oi the impregnation vessel,at which the surrounding surplus d digesting liquid is dischargedthrough the duct 18, the vessel is provided with a perforated innerjacket 39 which retains the impregnated fibrous materials, but allowsthe liquid to pass through.

The fibrous materials impregnated with digesting liquid are heaped up toa point 40 in the digesting vessel 3. By admission of heating steamthrough a duct 41 adjoining the lower part of the digesting vessel 3,the materials are brought to the necessary digesting temperature. Thedelivery of the completely digested material takes place continuouslythrough a delivery branch 42 having a gate valve 43.

For discharging any condensate which may be formed above the level 9 ofthe digesting liquid in the limb 2 of the impregnating vessel by theheating steam supplied, a further duct 45 having a valve 46 disposedtherein is connected to a point 44 above the point 19 at which thereflux duct 18 for the digesting liquid is connected.

It may prove advantageous to return the surplus digesting liquid from alower point, for example from the point 28 of the limb 2 of theimpregnation vessel, in order that the digesting liquid to be returnedmay not be heated by heating steam coming from the digesting chamber.The temperature of the digesting liquid which must be reintroduced intothe vacuum chamber is limited by the vacuum which must be maintainedtherein. If desired, cooling of the liquid returned through the duct 18into the introduction container 10 may be considered.

What is claimed is:

1. In a process for the treatment of fibrous materials in the productionof cellulose or semi-cellulose in which the fibrous materials areimpregnated with digesting liquid and digested at superatmosphericpressure and elevated temperature, the method of impregnating saidmaterials comprising the steps: continuously circulating an excessquantity of digesting liquid in a closed flow path which includes first,second and third portions; subjecting said liquid to atmosphericpressure in said first portion of said flow path, to vacuum in saidsecond portion of said flow path and to at least atmospheric pressure insaid third portion of said flow path; continuously admixing the materialto be impregnated with the circulating digesting liquid in said firstportion; leading the so-obtained mixture to said second portion;separating part of the circulating material and liquid from one anotherduring circulation through the second portion; recombining the materialjust separated and the circulating liquid as the material leaves thesecond portion; separating the material from the circulating liquid insaid third portion of the path and replacing with new liquid the liquidwhich is absorbed and adsorbed by the material; and recirculating theliquid through the flow path.

2. The method defined in claim 1 in which said third portion of the flowpath is subjected to the digesting pressure of the process.

3. In apparatus for the treatment of fibrous materials 1:

separating digesting liquid from the entering mixture of fibrousmaterials and circulating liquid; a by-pass for reintroducing theso-separated liquid into the flow connection between the vacuum chamberand the separation chamber; means arranged in said separation cham-- betfor separating the treated material together with dig'estingliquidabsorbed and adsorbed by it from the circulating liquid; and a storagecontainer for digesting liquid connected with the circuit to supplydigesting liquid thereto.

4. The combination defined in claim 3 including a discharge conveyorarranged within the vacuum chamber to discharge the fibrous materialscontinuously into the flow connection which leads from the vacuumchamber to the separation chamber.

5. The combination defined in claim 3 including a digesting vesseloperating at superatmospheric pressure, and means afiording an openconnection from the separation chamber to said digesting vessel; and inwhich the means for circulating digesting liquid is in the fiowconnection between the vacuum chamber and the separation chamber.

6. An apparatus for impregnating fibrous materials with digesting liquidin the production of cellulose or semi-cellulose comprising a vacuumchamber in which the said materials are deaerated, said vacuum chamberhaving a supply conduit for the materials to be deaerated and adischarge conduit for the deaerated materials; an introduction containersubject to atmospheric pressure situated well below the bottom of saidvacuum chamber; a separation chamber, said supply conduit beingconnected at one end to said introduction container and opening at itsother end into the vacuum chamber at a point near the top thereof, saiddischarge conduit extending from the bottom of said vacuum chamber andopening into the separation chamber, at least a portion of the saiddischarge conduit extending downward from the vacuum chamber; a fiowconnection connecting the separation chamber with the introductioncontainer, a flow circuit being formed thereby which leads seriallythrough the introduction container, the supply conduit, the vacuumchamber, the discharge conduit, the separation chamber, said last-namedfiow connection, and again through the introduction container; means forsupplying digesting liquid to said circuit; pump means arranged in saidcircuit for circulating the supplied digesting liquid through sadcircuit; means for continuously supplying the materials to beimpregnated and deaerated to said introduction container and foradmixing them with the circulating liquid; means arranged in saidseparation chamber for separating the deaerated and impregnatedmaterials from the circulating liquid with the liquid absorbed andadsorbed thereby and for discharging them from the separation chamber; avacuum pump connected to the vacuum chamber and serving to remove airwhich separates from the fibrous materials; and means arranged in thevacuum chamber for regulating the discharge of the fibrous materialsindependently of the rate of flow of the circulating liquid.

7. The combination defined in claim 6 in which the means in the vacuumchamber regulating the discharge of fibrous materials comprises sievemeans for separating at least a part of the liquid from the mixture ofdigesting liquid and fibrous materials entering the vacuum chamberthrough the supply conduit; a by-pass channel through which theso-separated liquid is fed to the discharge conduit so as to serve astransport liquid and impregnating liquid for the materials leaving thevacuum chamber; and a conveyor for discharging the remaining materialand liquid into the discharge conduit.

8. The combination defined in claim 6 in which the means in the vacuumchamber regulating the discharge of fibrous materials comprises an innersieve jacket so arranged that the mixture of digesting liquid andfibrous materials flowing through the supply conduit is fed into theinterior of the sieve jacket, the sieve jacket being spaced from thewall of the vacuum chamber to define a space that communicates with thedischarge conduit; and a conveyor arranged to discharge material andliquid from the interior of the sieve jacket to the discharge conduit.

9. The combination defined in claim 6 including a digesting vessel inopen communication with the separation chamber, whereby the separationchamber is subjected to digesting pressure; and said pump means is inthe discharge conduit and raises the pressure of the circulating liquidto the digesting pressure.

10. The combination defined in claim 9 including a fluid pressure motorin the fiow connection between the separation chamber and theintroduction container, in which fluid pressure motor the circulatingliquid is allowed to expand from digestion pressure to substantiallyatmospheric pressure while doing work.

11. The combination defined in claim 10 in which the fluid pressuremotor is connected to drive the pump means.

References Cited in the file of this patent UNITED STATES PATENTS1,773,419 Baker Aug. 19, 1930 1,938,060 Wood Dec. 5, 1933 1,986,760Kreissler Jan. 1, 1935 2,093,267 Dunbar Sept. 14, 1937 2,668,110 SpencerFeb. 2, 1954 2,799,579 Messing July 16 1957 2,809,111 Durant Oct. 8,1957

1. IN A PROCESS FOR THE TREATMENT OF FIBROUS MATERIALS IN THE PRODUCTIONOF CELLOULOSE OR SEMI-CELLULOSE IN WHICH THE FIBROUS MATERIALS AREIMPREGNATED WITH DIGESTING LIQUID AND DIGESTED AT SUPERATMOSPHERICPRESSURE AND ELEVATED TEMPERATURE, THE METHOD OF IMPREGNATING SAIDMATERIALS COMPRISING THE STEPS: CONTINUOUSLY CIRCULATING AN EXCESSQUANTITY OF DIGESTING LIQUID IN A CLOSED FLOW PATH WHICH INCLUDES FIRST,SECOND AND THIRD PORTIONS, SUBJECTING SAID LIQUID TO ATMOSPHERICPRESSURE IN SAID FIRST PORTION OF SAID FLOW PATH, TO VACUUM IN SAIDSECOND PORTION OF SAID FLOW PATH AND TO AT LEAST ATMOSPHERIC PRESSURE INSAID THIRD PORTION OF SAID FLOW PATH; CONTINUOUSLY ADMIXING THE MATERIALTO BE IMPREGNATED WITH THE CIRCULATING DIGESTING LIQUID IN SAID FIRSTPORTION; LEADING THE SO-OBTAINED MIXTURE TO SAID SECOND PORTION;SEPARTING PART OF THE CIRCULATING MATERIAL AND LIQUID FROM ONE ANOTHERDURING CIRCULATION THROUGH THE SECOND PORTION; RECOMBINING THE MATERIALJUST SEPARATED AND THE CIRCULATING LIQUID AS THE MATERIAL LEAVES THESECOND PORTION; SEPARATING THE MATERIAL FROM THE CIRCULATING LIQUID INSAID THIRD PORTION OF THE PATH AND REPLACING WITH NEW LIQUID THE LIQUIDWHICH IS ABSORBED AND ABSORBED BY THE MATERIAL; AND RECIRCULATING THELIQUID THROUGH THE FLOW PATH.